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At least 19 recordsLinked to original sources
PubMedDate not supplied

Viscoelastic properties and dynamics of porcine gastric mucin.

Gastric mucin is a glycoprotein known to undergo a pH-dependent sol-gel transition that is crucial to the protective function of the gastric mucus layer in mammalian stomachs. We present microscope-based dynamic light scattering data on porcine gastric mucin at pH 6 (solution) and pH 2 (gel) with and without the presence of tracer particles. The data provide a measurement of the microscale viscosity and the shear elastic modulus as well as an estimate of the mesh size of the gel formed at pH 2. We observe that the microscale viscosity in the gel is about 100-fold lower than its macroscopic viscosity, suggesting that large pores open up in the gel reducing frictional effects. The data presented here help to characterize physiologically relevant viscoelastic properties of an important biological macromolecule and may also serve to shed light on diffusive motion of small particles in the complex heterogeneous environment of a polymer gel network.

Animals↗
PubMed2004

[A case of mucinous gastric adenocarcinoma as submucosal tumor].

Gastric mucinous adenocarcinoma is a rare histologic subtype of gastric cancers. It has been reported that the gross or endoscopic finding of mucinous gastric carcinoma is commonly described as a ulcerative or fungating mass in common. There has been controversy over the prognosis and the gross morphology of mucinous gastric adenocarcinoma. We report a case of mucinous gastric adenocarcinoma presenting as a submucosal tumor.

Adenocarcinoma, Mucinous↗
PubMed1997

Comparative rheological investigation of crude gastric mucin and natural gastric mucus.

Mucus is a viscoelastic gel covering the entire alimentary tract. It represents a pre-epithelial diffusion barrier influencing the drug absorption process. In this way the rheological properties of mucus play an important role. The purpose of our investigation was to evaluate and compare the rheological properties of rehydrated dried crude porcine gastric mucin (Sigma mucin) and isolated natural porcine gastric mucus. Two different rheological approaches were used: constant shear and oscillatory shear conditions. The results obtained under steady shear conditions show that the reduction of apparent viscosity is caused by time, shear rate and temperature. With increasing Sigma mucin concentration the rheological behaviour changes from time-independent systems fitting in with the Casson model to time-dependent systems fitting in with the Herschel-Bulkley rheological model. Measurements performed under oscillatory shear conditions clearly show how the mechanical response of different concentrated systems has changed from dispersions with prevailing plastic to prevailing elastic properties. Mechanical deformation and frequency response of natural gastric porcine mucus have shown a strong gel structure with elastic properties. Comparing both systems it can be concluded that after rehydration of dried crude gastric porcine mucin, a model mucus system with rheological properties equivalent to natural mucus cannot be obtained.

Animals↗
PubMed1974

Binding of cholera toxin to mucins and inhibition by gastric mucin.

The effects of mucin on cholera toxin induced intestinal secretion was studied in the rat small intestine. Gastric mucin inhibited secretion when premixed with cholera toxin on an equal dry-weight basis. Neither salivary nor intestinal mucin inhibited the toxin's action in the intestine. Inhibition by gastric mucin was not reversed by a mucolytic agent or by hexoses or agents that bind hexoses. Plasma and serum did not inhibit the effects of cholera toxin in the intestine. Choleragen was labeled with (14)C and its binding to mucins and ganglioside was studied. Gastric mucin was shown to bind to choleragen, but less binding was observed when choleragen was dissociated into subunits by acid pH. Salivary and intestinal mucins bound intact choleragen but not the subunits at acid pH. Salivary mucin binding was reversed by N-acetyl neuraminic acid and neuraminidase. Ganglioside bound choleragen in both the intact and dissociated forms. Binding to the dissociated form was reversed by wheat germ agglutinin. Gastric mucin and ganglioside competed for binding to choleragen with the binding of intact choleragen greater for ganglioside and the affinity of the subunits greater for gastric mucin. Electrophoresis of labeled choleragen showed uniform labeling of the subunits dissociated by acid pH, but a major part of cholera toxin was found not to be labeled when fractionated with sodium dodecyl sulfate and 2-mercaptoethanol.

Animals↗
PubMed1983

Cysteamine and prostaglandin F2 beta stimulate rat gastric mucin release.

Gastric mucin glycoproteins form an adherent gel over the surface epithelium that is thought to protect the stomach against chemical and physical damage. The purpose of this study was to measure the release of mucin glycoproteins from rat stomach after treatment with cysteamine and prostaglandin F2 beta, two structurally unrelated drugs that have been shown to protect the stomach against the noxious effects of alcohol and other damaging agents. Gastric mucin was separated into soluble (washout) and insoluble (adherent) phases before colorimetric quantitation of total mucin, protein-bound hexose, and sialic acid. Cysteamine produced a dose-dependent increase in release of soluble and gel mucin. Prostaglandin F2 beta caused a dose-dependent release of hexose-containing mucin but had no effect on sialic acid-containing glycoproteins. Sepharose 4B chromatography of both the soluble and adherent mucus revealed that greater than 90% was a high molecular weight glycoprotein fraction. N-Ethylmaleimide, a known inhibitor of cytoprotection by cysteamine, had no effect on mucin secretion. Similarly, indomethacin inhibited mucin secretion by cysteamine but did not significantly influence cytoprotection. Thus the secretion of mucin by cytoprotective agents is unlikely by itself to explain the ability of the stomach to resist chemical or physical damage.

Animals↗
PubMed2001

Does Helicobacter pylori affect gastric mucin expression? Relationship between gastric antral mucin expression and H. pylori colonization.

BACKGROUND/OBJECTIVE: Helicobacter pylori colonizes the gastric mucous gel layer, the surface epithelium and glands. It has been shown that H. pylori infection causes aberrant expression of gastric mucins MUC 5 and MUC 6. This study aimed to determine the distribution of MUC 5 and MUC 6 in the gastric antrum of dyspeptic patients, and to investigate changes in this pattern in the presence of H. pylori and after successful eradication. MATERIALS AND METHODS: Gastric antrum biopsy specimens were examined by immunohistochemistry for mucin gene (MUC 5 and MUC 6) expression. Polyclonal antibodies were used to detect amino acid tandem repeats of each protein. A scoring system (0-3) was used to assess staining intensity at three sites: foveola, mucous neck cells and glands. H. pylori status was determined by histology and rapid urease test, and considered positive or negative when both tests were positive or negative, respectively. The study included 49 patients positive for H. pylori, in 36 of whom successful eradication was performed, and 11 H. pylori-negative patients. RESULTS: There was a gradient of MUC 5 expression, higher to lower, from the surface to the glands, which was more pronounced before eradication. Increased MUC 5 synthesis in the mucous neck cells and in the glands was found after H. pylori eradication (P = 0.016). MUC 6 was synthesized in the glands more than in the mucous neck cells or foveola. MUC 6 was also secreted into the lumen and probably comprised the superficial part of the unstirred mucous layer. CONCLUSION: The change in MUC 5 synthesis may reflect H. pylori colonization.

Adult↗
PubMed2006

Hath1 up-regulates gastric mucin gene expression in gastric cells.

The Notch signaling pathway is known to mediate the differentiation and fate specification of cells in embryonic stage and adult tissues. Several tumors exhibit aberrant expression of Notch signaling component genes, such as Notch1/2/3 and Hath1. In this study, we investigated the mRNA expression of seven Notch-related genes, Notch1/2/3, Hes1/2/3, and Hath1, and then compared it with the expression of gastric mucin genes, MUC5AC and MUC6, in eight gastric cancer (GC) cell lines. Notch1/2/3 and Hes1 were expressed in most GC cell lines as well as normal gastric mucosae, while Hes2/3 were expressed in neither these cell lines nor the normal stomach. As for Hath1, five GC cell lines exhibited undetectable levels, while normal gastric mucosa expressed Hath1. The expression patterns of Hath1 and MUC6 were closely related in most GC cell lines. Many MUC5AC-positive cases also tended to show Hath1 expression. Over-expression of Math1, a mouse Hath1 homolog, in the GC cells strongly enhanced both the MUC6 and MUC5AC mRNA levels. Moreover, knockdown of Hath1 by means of RNA interference significantly decreased the expression of both mucin genes. These data indicate that Hath1 is one of the transcriptional regulators for MUC6 and MUC5AC in GC cells. It is also possible that loss of Hath1 expression may play a role in gastric carcinogenesis.

Animals↗
PubMed1995

Mouse gastric mucin: cloning and chromosomal localization.

Mucins protect gastric epithelium by maintaining a favourable pH gradient and preventing autodigestion. The purpose of this study was to clone a mouse gastric mucin which would provide a foundation for analysis of mucin gene regulation. Mucin was purified from the glandular portion of gastric specimens and deglycosylated by HF solvolysis. Antibodies against native and deglycosylated mouse gastric mucin (MGM) were raised in chickens. Screening of a mouse stomach cDNA library with the anti-(deglycosylated MGM) antibody yielded partial clones containing a 48 bp tandem repeat and 768 bp of non-repetitive sequence. The 16-amino-acid tandem repeat has a consensus sequence of QTSSPNTGKTSTISTT with 25% serine and 38% threonine. The MGM tandem repeat sequence bears no similarity to previously identified mucins. The MGM non-repetitive region shares sequence similarity with human MUC5AC and, to a lesser extent, human MUC2 and rat intestinal mucin. Northern blot analysis reveals a polydisperse message beginning at 13.5 kb in mouse stomach with no expression in oesophagus, trachea, small intestine, large intestine, caecum, lung or kidney. Immunoreactivity of antibodies against deglycosylated MGM and against a synthetic MGM tandem repeat peptide was restricted to superficial mucous cells, antral glands and Brunner's glands in the pyloric-duodenal region. DNA analysis shows that MGM recognizes mouse and rat DNA but not hamster, rabbit or human DNA. The MGM gene maps to a site on mouse chromosome 7 homologous to the location of a human secretory mucin gene cluster on human chromosome 11p15. Due to sequence similarity and predominant expression in the stomach, the MGM gene may be considered a MUC5AC homologue and named Muc5ac.

Amino Acid Sequence↗
PubMed1998

Histochemical analysis of mucous cells of congenital adenomatoid malformation of the lung: insights into the carcinogenesis of pulmonary adenocarcinoma expressing gastric mucins.

Adenocarcinomas expressing gastric mucins often are accompanied by ectopic gastric mucosa or pyloric metaplasia. We have previously described mucinous bronchioloalveolar carcinoma (mucinous BAC) producing gastric mucins. In the lung tissue, mucous cells seemingly similar to gastric mucous cells are present in congenital adenomatoid malformation (CAM). We assessed 26 cases of CAM morphologically and histochemically. Mucous cells were detected in 12 of 26 cases. These mucous cells displayed papillary growth in cystic spaces and proliferated along alveolar walls. Mucous cells in the papillary, configuration stained with galactose oxidase cold thionine Schiff reaction, and those in indented portions stained with paradoxical concanavalin A stain in all 8 cases and with pepsinogen II in 5 of 8 cases, which were available for histochemical analysis. Pepsinogen I was negative. Mucous cells in CAM were identical to those of pyloric mucosa and could be considered candidates for the origin of mucinous BAC producing gastric mucins.

Adenocarcinoma, Bronchiolo-Alveolar↗
PubMed1991

The oligomeric structure of rat and human gastric mucins.

Intact oligomeric gastric mucins were isolated from the fundic part of rat and human stomach. Physicochemical properties of the oligomeric mucins from both species, such as buoyant density, molecular mass, proteinase-resistance, amino acid composition and monosaccharide composition were similar. Biochemical analysis showed that the oligomeric mucins from both species consist of disulphide-linked mucin monomers exclusively: no other covalently attached proteins were detected in purified monomeric mucin. Four major differences were found between the monomeric mucins of these species: (1) the human monomer is larger, (2) the proteolytic-digest peptides derived from proteinase-sensitive portions of the polypeptide backbone displayed no sequence similarity, (3) the human mucin was less sulphated compared with rat mucin, and (4) the proteinase-sensitive part of the human mucin was relatively larger. However, analyses of [3H]galactose-labelled mucin from both species on gel filtration revealed that both gastric mucins were exclusively synthesized as oligomers. The results indicate that the oligomeric structures of human and rat gastric mucin are similar and their biosyntheses are not affected by the differences in the subunits.

Amino Acids↗
PubMed1996

Effects of traditional herbal medicine on gastric mucin against ethanol-induced gastric injury in rats.

The effect of the traditional herbal medicine, Rikkunshi-to and its component crude drugs, Zingiberis Rhizoma and Glycyrrhizae Radix, on the gastric mucin was studied using a method developed to separate and quantify the mucin localized in the different layers of rat gastric mucosa. The oral administration of spray-dried extract to Rikkunshi-to (1000 mg/kg), Zingiberis Rhizoma (500 mg/kg) and Glycyrrhizae Radix (500 mg/kg) significantly prevented gastric mucosal damage induced by 70% ethanol in rats. In ethanol-treated rats the mucin content of the deep mucosa was reduced, and the reduction of the deep corpus mucin content was significantly inhibited by pretreatment of Rikkunshi-to and Zingiberis Rhizoma. Rikkunshi-to and Glycyrrhizae Radix pretreatment increased the surface mucin content by 140 and 146%, respectively. The effect on the gastric mucin by each drug differed in the different layers of the gastric mucosa.

Administration, Oral↗
PubMed1999

Fragmentation pattern of mucins in normal and diseased gastric mucosae: a glycoprotein fractionates with gastric mucins purified from mucosal scrapings of cancer and peptic ulcer patients.

BACKGROUND/AIMS: Gastric cancer, a fatal malignancy, is prevalent in the Western Cape region of South Africa. The aim of this study was a biochemical characterisation of gastric mucins in this disease, compared with gastric ulceration and controls from transplant donors. METHODS: Mucins were extracted in a denaturing medium (to prevent endogenous proteolysis) and purified by caesium chloride density gradient ultracentrifugation. Analysis of mucin was by gel filtration, SDS-PAGE and Western blotting methods. RESULTS: All samples of mucin when analysed by gel filtration were found to contain polymeric glycoprotein together with varying amounts of lower-molecular-weight glycoprotein. SDS-PAGE and Western blot analysis showed that diseased stomachs had glycopeptides of a wider range in size and antigenicity with a greater number of smaller fragments immunoreactive to monoclonal antibodies 2-12M1 and 9-13M1. We identified by SDS-PAGE a glycoprotein which co-fractionates in a caesium chloride density gradient with mucins isolated from gastrectomy specimens resected for carcinoma and peptic ulceration and which was absent from mucins of the transplant donor control group. This neuraminidase-sensitive glycoprotein resisted dissociation from mucin during purification in a 3.5 M CsCl density gradient but was partially separable by Sepharose 2B gel chromatography and heat treatment (100 degrees C, 2.0 min) in SDS. Chemical analysis of the glycoprotein by HPLC favours it being an N-linked glycoprotein. Its non-ideal electrophoretic properties make its exact size estimation difficult and we ascribe to it a broad size range of Mr approximately 55-65 kD. CONCLUSION: We conclude that mucins from diseased stomachs were more degraded than those from donors and that the diseased mucosa reproducibly secretes a Mr approximately 55-65 kD glycoprotein, the role of which needs to be established.

Adenocarcinoma↗
PubMed1998

Helicobacter pylori infection produces reversible glycosylation changes to gastric mucins.

The protective ability of gastric mucins may depend largely on their oligosaccharide chains. We evaluated the effects of H. pylori infection on the glycosylation of gastric mucins. Gastric biopsy specimens from 20 H. pylori-infected patients before and after cure of the H. pylori infection and 8 normal uninfected volunteers were examined by immunostaining for simple mucin-type glycoproteins and blood-group-related antigens bearing type 1 chain backbone. The immunoreactivity in different gastric compartments was evaluated. Simple mucin-type glycoproteins and blood-group-related antigens were expressed in surface mucous cells. Simple mucin-type glycoproteins showed antrum-predominant expression in normal volunteers and were found in significantly fewer surface mucous cells in infected patients than in normal volunteers; their expression was restored after eradication of H. pylori. Sialyl Lewis(a) and Lewis(b) were expressed in fewer surface mucous cells after than before eradication. The patterns of glycosylation of gastric mucins vary in different gastric compartments and are reversibly altered by H. pylori infection. These alterations may affect the protective functions of gastric mucins.

Adult↗